Engineering Innovation

Maddy O’Neal held a shiny titanium screw in her hand while studying a computer model of the device on the screen in front of her, looking for potential weaknesses once the screw is put in someone’s body to repair a broken hip. “There are lots of ways these can fail,” says O’Neal, a senior majoring in biomedical engineering. “The screws can come out and float around in someone’s body. There are a lot of moving parts, which is a good thing and a bad thing.”

The device O’Neal is evaluating is one of several types designed to help mend broken hips that have one feature in common—a history of breaking. Improving those flawed devices is a challenge that O’Neal and her classmates have attempted to resolve this semester. O’Neal is among 20 undergraduate students in the medical device design class, which is offered by Yale School of Engineering and Applied Science. The course combines medicine, engineering, and problem-solving with the goal of improving unreliable devices.

Broken screws are a problem. In the case of one model, the shaft that runs along the femur can fail where the bone is broken. The bone is not supporting the patient’s weight at that point—the metal shaft must do it. Sometimes the shaft is not up to the task, says Alexander Crich, a senior majoring in biomedical engineering and mechanical engineering, as he held the implant in front of him.

Students do much of their work with computer modeling software, but real-world experiences are an important part of the class. Accompanying one of the course directors, Daniel Wiznia, MD, in the operating room, students get a sense of the surgery in which the implants and screws are installed.

Another lecture features a presentation from Kristaps J. Keggi, MD ’59. A professor emeritus and senior research scientist of orthopaedics and rehabilitation in the medical school, Keggi has performed over ten thousand hip-replacement surgeries and consulted for companies that produce the implants. He told students the work they are doing has been going on since the 19th century, when early implants were made of ivory or wood. Keggi told students that physicians have played a key role in improving implants. While the students are using sophisticated computer software for their projects, Keggi says he once sketched the preliminary design for an implant on a napkin in a restaurant while on a business trip in Cleveland.

“We learned as we were using them,” Keggi says of the implants.

This is the fifth year the engineering school has offered the medical device design class. In previous years, students were asked to come up with an idea for a new device. Proposals included a lab coat sanitizer and technology aimed at helping people recover from concussions.

Steven Tommasini, PhD, a research scientist of orthopaedic rehabilitation at Yale School of Medicine who is co-teaching this semester’s class, says that this year students are focused on improving existing devices. Hip implants were chosen because procedures for that part of the body are common, Tommasini says.

“Compared to other implants they are relatively simple. Also, they are in a spot that is the most heavily loaded spot in the body, so failure is not uncommon,” he says.

Students are divided into teams charged with studying one of five different implants used to treat hip fractures. Each of these devices is on the market, but they have unique strengths and weaknesses for treating different fracture patterns, Tommasini says. The students use computer modeling to simulate the stresses on each implant to figure out where and how it fails. With that information, they can turn their attention to designing a better implant.

After studying the hip screws, the students model different kinds of artificial hip joints used for total replacement procedures. After that, they can choose their own idea for the final part of the class, Tommasini says. He teaches the class with Wiznia, who is an assistant professor of orthopaedics at the medical school as well as an assistant professor of mechanical engineering and materials science at Yale School of Engineering.

Wiznia says students are studying how well these hip implants treat an uncommon injury called a subtrochanteric fracture. This kind of fracture can result from an accident but is also seen in patients taking bisphosphonate therapy for osteoporosis. Although the implants are customarily used to fix this kind of fracture, Wiznia says that the implants were not designed for it. “They do an okay job, but they have a failure rate.”

The class was not going to be held in the spring semester because of a scheduling conflict but was put on the schedule anyway after widespread student demand. “I was excited to take a class where you design something, get your hands dirty, and solve a problem,” says Matan Cutler, a sophomore.

“They needed someone to take over this class and we’re hoping we can keep doing it because we’re having fun,” Tommasini says. “This is one of the few classes where you get to build something and be creative. Engineering students don’t get to do that a lot.”

Wiznia says the class is a good way of bringing together two disciplines that can help each other.

“As an engineer, you are a problem solver,” he says. “As a surgeon, you are constantly trying to improve medical outcomes. This is a terrific fit for an engineer.”

Most of the students who take the class are in the engineering department. Lauren Ribordy, a senior majoring in biomedical engineering, says she was excited to use the computer modeling technology but also found it sobering to find out more about bone fractures. “There is a lot of potential to help people,” Ribordy says. “It should not be a case of ‘We hope it will work.’ Can we model it to see if it will fail before we give it to a patient?”

O’Neal says she wants to go into the medical field and work with implants. Initially she was interested in prosthetics but shifted her interest to hip devices, in part because of the experience of her grandmother who, she says, had both knees and a hip replaced. She also sees a growing need for better technology to repair joints.

“This is really what I want to do, implants or something like that. They are so cool,” O’Neal says. “As people get older our bodies are more likely to fracture; and now athletes are getting knee replacements that need to stay in place for 30 or 40 years. With people living longer, implants won’t be going anywhere.”